1. Field of the Invention
This invention pertains to a method for recovering petroleum from subterranean petroleum-containing formations. Particularly, this invention relates to a method of treating underground formations containing clays or clay like material to increase or reestablish water permeability of the clay. More particularly, this invention relates to an improved secondary recovery process wherein petroleum is displaced from a formation by flooding the formation with an aqueous solution containing a polysaccharide in sufficient quantity to increase the viscosity of the solution, a water soluble guanidine compound and a naturally occurring salt.
This invention is particularly useful in improving or reinstating the production of petroleum in formations that have been partially depleted by primary recovery techniques or where the communication between the injection well and the production well has been restricted by the swelling of water-sensitive clays in the formation.
2. Description of the Prior Art
The production of petroleum is usually accomplished by drilling into a petroleum containing formation and utilizing one of the well known methods for the recovery of petroleum. However it is recognized that these primary recovery techniques may recover only a minor portion of the petroleum present in the formation particularly when applied to formations containing viscous petroleum. In such cases, secondary recovery methods are called for. Among the methods employed in secondary recovery operations are water flooding, steam injection, gas flooding and combinations thereof. One of the most serious problems encountered in secondary recovery operations with water flooding or steam injection procedures is that the underground oil-containing formation also contains clay or clay like bodies associated therewith. Treatment of such a formation with water or steam generally results in swelling of the clay by absorption of the water, with the concomitant result that the water permeability of a formation is materially decreased. The decrease in the permeability of the formation to water causes a reduction in the amount of oil which can be recovered by secondary recovery operations.
It is known from the prior art; U.S. Pat. Nos. 3,360,043 and 3,444,931, that clay containing formations can be treated to improve the water and/or steam permeability of the clay by contact with a guanidine salt dissolved in various hydrocarbon solvents.
Another problem which reduces the total effectiveness of water flooding operations is poor sweep efficiency. Poor sweep efficiency is associated with the inability to contact all of the petroleum containing flow channels with the injected aqueous fluid. Poor sweep efficiency results primarily from an adverse mobility ratio. The injected aqueous fluid generally has a substantially lower viscosity at reservoir conditions than the viscosity of the formation crude which it is intended to displace. A low viscosity fluid will not displace a high viscosity fluid uniformly and there is tendency for the injected low viscosity fluid to channel into the high viscosity fluid and bypass a substantial portion of high viscosity fluid. The displacement efficiency is improved substantially if the injected fluid viscosity is increased to a value greater than the displaced fluid viscosity. This problem has also been recognized by persons skilled in the art of oil recovery, and various additives have been proposed to increase the viscosity of the injected fluid in order to improve the sweep efficiency. Hydrophilic polymers which have the effect of increasing the viscosity of the displacing fluid improve the mobility ratio and decrease the tendency for the injected fluid to channel into and inefficiently displace the higher viscosity petroleum. For example, U.S. Pat. No. 3,372,749 (1966) discloses the use of a polysaccharide to increase the viscosity of injected water to improve the displacement efficiency of water flooding type oil recovery processes. Polysaccharides such as are produced by microbial action on natural carbohydrates are shown in the prior art for this purpose.